In general, a signal receiver circuit in an integrated circuit (IC) such as a semiconductor device may receive a reference voltage signal and a plurality of input signals from an external device and amplify the input signals. The signal receiver circuit may compare the input signals with the reference voltage signal to generate a control signal for controlling an internal circuit included in the IC. The control signal may have a logic level which is determined according to a comparison result of the input signals and the reference voltage signal. For example, the control signal may be set to have a logic “high” level when a logic level of the input signal is higher than that of the reference voltage signal and the control signal may be set to have a logic “low” level when a logic level of the input signal is lower than that of the reference voltage signal. The reference voltage signal inputted to the signal receiver circuit should be set to have a median level between a predetermined maximum level (VILmax) and a predetermined minimum level (VILmin). However, the reference voltage signal may vary depending on the circumstance. For example, the reference voltage signal may have an abnormal level due to an environment condition, noises of power signals of a system, interconnection shapes of a printed circuit board (PCB) and/or interconnection shapes of a package device. If the reference voltage signal has an abnormal level, the signal receiver circuit may incorrectly recognize a level of the input signal to generate an erroneous control signal having an incorrect logic level and to cause a malfunction of the internal circuit. Thus, it may be necessary to accurately adjust or minimize a level fluctuation of the reference voltage signal in order to prevent a malfunction of the semiconductor IC.